In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display board or the like, a pattern is made by irradiating a light to a semiconductor wafer or an original plate for liquid crystal, but if a dust is attached a photo mask or a reticle (hereinafter collectively referred to as “photo mask” for simplicity) which is used during the irradiation operation, the dust causes the pattern to have roughened edges or black stains on a base, and thus leads to problems such as damaged dimensions, poor quality, and deformed external appearance.
Thus, these works are usually performed in a clean room, but it is still difficult to keep the photo mask clean all the time. Therefore, a pellicle is attached to a surface of the photo mask as a dust-fender before photo irradiation is carried out. Under such circumstances, foreign substances do not directly adhere to the surface of the photo mask but adhere only to the pellicle membrane, which is sufficiently away from the photo mask surface so that by setting a photo focus on a lithography pattern on the photo mask, the foreign substances on the pellicle membrane fail to transfer their shadows on the photo mask and thus no longer become a cause for problems to the image transfer performance.
In general, a pellicle is made by tensely adhering a transparent pellicle film made of a highly light transmitting material such as cellulose nitrate, cellulose acetate, fluorine-containing polymer and the like to one of the two annular frame faces of a pellicle frame made of aluminum, stainless steel, polyethylene or the like, using as the glue either a solvent capable of dissolving the pellicle film, which is applied to said annular frame face (hereinafter this face is called “upper frame face”) and then air-dried before receiving the film (ref. Japanese Patent Application Publication S58[1983]-219023), or an adhesive such as acrylic resin, epoxy resin or the like (ref. U.S. Pat. No. 4,861,402 and Japanese Pre-Patent Publication for Public Review S63[1988]-27707). The other annular frame face (hereinafter called “lower frame face”) of the pellicle frame is paved with an agglutinant made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin or the like for attaching the pellicle frame to a photo mask, and over this agglutinant layer is laid the release liner (tape) to protect the agglutinant layer.
This release liner is constituted by a base sheet and a parting agent applied to at least one face of the base sheet, and it is required to have a sufficient releasability from the agglutinant layer of the pellicle. The parting agent may be suitably selected depending on the kind of the agglutinant used in the pellicle. For example, in the case of a silicone agglutinant, which is excellent in light resistance, a fluorine-modified silicone parting agent is favorably used, and in the case of an acrylic agglutinant, a silicone parting agent is favored.
IP Publication 1 described a highly releasable liner for pellicle agglutinant, in which a fluorine-modified silicone parting agent is applied to at least one face of the base sheet in an amount of 0.1-1.0 g/m2.